Heat exchangers can be used to transfer heat from one liquid or gas stream to another liquid or gas stream. Within the heat exchanger, the streams are separated by a wall that is typically constructed of heat conducting metal. Various types of heat exchangers can be utilized (e.g., shell and tube heat exchanger, plate-and-frame heat exchanger, finned coil heat exchanger, and so forth). A heat exchanger's capacity is limited by, for example, its size, the flow rate of the streams, and the temperature difference between the streams. A minimum temperature difference between the streams (the approach temperature) is typically approximately 5 degrees Celsius. Heat exchangers can be operated under pressure to keep the streams in a liquid phase.
An ethanol production plant is an example of a facility that utilizes heat exchangers. Ethanol can be produced from grain-based feedstocks (e.g., corn, sorghum/milo, barley, wheat, etc.), from sugar (e.g., sugar cane, sugar beets, etc.), or from biomass (e.g., lignocellulosic feedstocks, such as switchgrass, corn cobs and stover, wood, or other plant material). An ethanol facility that produces ethanol from corn typically employs a process wherein corn is ground to a flour, mixed with water and enzymes to break down the starch contained in the corn into sugar (e.g. glucose) and fermented into a fermentation product by yeast. The ethanol is recovered from the fermentation product in a distillation system and is dehydrated using molecular sieves. Many unit operations within the ethanol production process require temperature control. For example, streams, such as the fermentation product (e.g., beer), process water, different ethanol streams, and distillate are typically cooled or heated through the use of heat exchangers. An ethanol production facility may experience seasonal changes in the need for cooling capacity. For example, during the warmer months an ethanol production facility typically will experience an increased need for cooling capacity.